1. Field of the Invention
This invention relates to a control system for use with a multistable suspension unit.
2. Disclosure Information
Multistable automotive suspension units have been known for some time. The present control system is suitable for use with a multistable unit of the type disclosed in U.S. Pat. No. 4,313,529 in which a hydraulic mechanism. The damping force is rendered adjustable by a damper is provided with a damping force adjusting rotary valve positioned within a passageway extending through the damper's piston. The rotary valve is connected to a potentiometer which is arranged such that its output matches that of a reference signal when the desired position of the shock absorber has been reached. This damper is defined as "multistable" for the purposes of this application because it has a plurality of predetermined states in which it may be selectively operated.
Multistable suspension units are intended to provide adaptive control of vehicle ride and hangling. In typical fashion, the particular state chosen for the multistable unit is determined by a control algorithm with inputs from a variety of vehicle parameters. For example, it is known to control a multistable suspension unit by utilizing vehicle linear acceleration, braking, steering activity, and vehicle speed, as well as through a manually operable mode switch. Known systems trigger a "firm" setting for a multistable suspension unit when the vehicle's speed exceeds a given value, or when the brakes are applied, or when lateral acceleration (turning) is sensed.
U.S. Pat. No. 2,140,767 discloses means for controlling shock absorber firmness as a function of intake manifold vacuum. Intake manifold vacuum is correllatable under certain conditions with vehicle acceleration, but is not reliable indication of acceleration for vehicles equipped with diesel engines or certain other engines equipped with turbocharger or fuel injection equipment which may limit or even totally eliminate intake manifold vacuum.
U.S. Pat. No. 3,861,696 discloses an amplitude responsive active damper system in which damping is increased as the magnitude of the vehicle's angular velocity increases. This system is intended to prevent rocking of the vehicle.
Examples of systems in which shock absorber rates are controlled solely by brake operation are disclosed in U.S. Pat. Nos. 3,537,715 and 3,548,977. U.S. Pat. Nos. 2,698,068 and 3,146,862 disclose systems in which brake line pressure operates upon piston and sliding valve arrangements designed to vary the flow area of fluid through modified shock absorbers so as to reduce brake dive. None of these systems is adaptive because none may be preferentially employed. More specifically, each is responsive to brake pressure and therefore actuates whenever brake pressure is present, regardless of any other operating conditions.
U.S. Pat. Nos. 3,608,925 and 4,345,661 illustrate use of steering input and control of suspension units. A related type of control is disclosed in U.S. Pat. No. 3,895,816 in which a centrifugal force sensor is operatively associated with valving to bias the vehicle so as to prevent excessive body roll during cornering. Systems employing fixed steering angle sensors are prone to failure due to misadjustment of the sensor inasmuch as precise angular measurements must be obtainable from such sensors if they are to be employed in systems capable of correcting or anticipating and preventing excessive roll of an automobile body during a cornering maneuver. A related problem affects systems employing centrifugal force sensors inasmuch as such forces cannot be sensed until they exist and once such force has come into existence the vehicle's body will typically have assumed an attitude which can be corrected only by an active suspension device capable of exerting force independent of its velocity of operation. Thus, to be effective, a device for providing input to a control system for operating a suspension unit should anticipate lateral acceleration rather than merely sense acceleration.
U.S. Pat. Nos. 3,146,862 and 3,548,977 illustrate the use of vehicle speed as an input to a system for modulating vehicle shock absorber performance.
U.S. Pat. Nos. 1,930,317 and 3,548,977 disclose the use of manually operable means for varying shock absorber settings.
U.S. Pat. No. 4,468,050 discloses a variable rate automotive suspension system that is controlled in accordance with a software routine stored in a computer to compensate for changes in road conditions and to reduce roll and pitch during cornering. This system uses a sensor associated with each of the controllable shock absorbers to determine the position of the axle with respect to the chassis; it does not use a sterring wheel sensor.
U.S. Pat. Nos. 3,913,938; 4,333,668; and 4,345,661 disclose vehicle suspension systems having shock absorbers which are controlled in response to the roll and pitch of the vehicle. These systems do not utilize the control parameter of vehicle steering input.
U.S. Pat. Nos. 4,371,191 and 4,519,627 disclose control systems for adjusting various vehicle suspension parameters wherein the control systems utilize several inputs, including steering direction. In each case, there is no calculation of a steering straight-ahead reference position in the control system. Certain prior art steering systems are believed to suffer from yet another deficiency inasmuch as steering excursions grewater than 180 degrees of steering wheel travel may confuse the system by creating a false indication that the steering system is returning to the center position.
U.S. Pat. No. 4,526,401 discloses an electronic control system for a shock absorber in which a detector and comparator combination is employed for the purpose of establishing that a motor drive unit has properly positioned the shock absorber at the desired degree of firmness.
It is an object of the present invention to provide a control system for a multistable suspension unit which control system utilizes the parametric inputs of vehicle speed, linear acceleration, (including braking), and calculated lateral acceleration.
It is another object of the present invention to provide a control system for a multistable suspension unit including a steering sensor which dynamically determines a center position.
It is yet another object of the present invention to provide a control system for a multistable syspension unit including a steering sensor which requires no recalibration to permit precise operation throughout its useful life.
It is a further object of the present invention to provide a control system for a multistable suspension unit including feedback sensing of the position state of the multistable suspension unit.